The nutritive value of Tipuana tipu and Calliandra calothyrsus as supplements to low-quality straw for goats

Abstract

Twenty-four Australian cashmere goats (32–40 kg live-weight (LW)), held in separate metabolism cages, were used in an experiment with a 2×4 factorial arrangement of treatments to study the effects of supplements of the dried leaves (browse) from two species of fodder tree ( Tipuana tipu, and Calliandra calothyrsus ) at four different levels (0, 0.83, 1.66% LW and ad libitum) on voluntary intake and utilisation of a basal diet of barley straw (BS). A supplement of urea–molasses (UM) (30 g urea, 70 g molasses) was given to control goats (0% browse), and both these goats and those given browse supplements consumed BS ad libitum. The basal diet of barley straw plus UM was consumed in limited amounts (41 g/kg 0.75 day) and was of low DM digestibility (47–53%). At the lowest level of Tipuana supplementation (0.83% LW, 27% DM intake), voluntary consumption of BS was significantly increased above basal, resulting in a 50% increase in total intake, and 73% in digestible DM intake. When Tipuana supplements were increased to 1.66% LW (56% DM intake), BS intakes decreased to the same extent that the supplement increased , resulting in no further improvement in either total intake or efficiency of diet use. When Tipuana was offered as the sole feed, total voluntary intake and digestible DM intake reached a maximum (66.4 and 42.0 g/kg 0.75 per day, respectively), and from a consideration of all aspects of this evaluation, Tipuana tipu compared very favourably with other high-quality browse species. However, Calliandra calothyrus proved to be of less value. The lowest level of supplementation resulted in a small increase in total (18%) and digestible DM (19%) intakes, but a decreased digestibility and availability of N for absorption and use. Further increases in supplement increased digestible intake, but N availability remained low and limiting. When Calliandra was offered as the sole diet ad libitum, total and digestible DM intakes (45.6 and 21.6 g/kg 0.75 per day) were no better than the control (barley straw plus UM) diet (41.5 and 22.0 g/kg 0.75 per day) and may be characterised as low in nutritive value and, in comparison with other browse species, of limited value as either a supplement or sole feed for ruminants in the tropics.